This research is an investigation of the interrelationships between tumor formation in the thyroid gland and thyroid hormones. Our immediate aim is to make a quantitative study of the thyroid hormones, their precursors and metabolites, in normal and abnormal human and rat glands, making use among other techniques of our newly developed method of gas chromatography. Our long-term goal is to define the biochemical changes occurring during benign and malignant tumor formation in the thyroid gland.